Inheritance of Genes in Bacteria: 2

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Bacterial genomes vary greatly in size, and some are __.

The E. Coli genome has an __. There is great variation among bacterial genomes

These sizes reflect the __

linear DNA molecules

average size

number of genes that the bacterium possesses, which in turn reflects lifestyle

The E. coli genome is a __; it is similar for other bacterial genomes

__ can also be found

Linear molecules have __, which must be distinguishable from __, so these chromosomes require __

single, circular DNA molecule

Linear versions

free ends

DNA breaks

terminal structures equivalent to the telomeres of eukaryotic chromosomes

In Borrelia and Agrobacterium, the real chromosome ends are distinguishable because a __, and in Streptomyces the ends appear to be __

covalent linkage is formed between the 5’ and 3’ ends of the polynucleotides in the DNA double helix

marked by special binding proteins

Some bacteria have multipartite genomes—__

With this, there is difficulty in __

Because the genes carried by a plasmid are __, the bacterium being able to survive without them, a plasmid is generally looked on as an __ rather than a genuine part of a bacterium’s genome

genomes that are divided into two or more DNA molecules

distinguishing a genuine part of a genome from a plasmid

nonessential

accessory molecule

When there is a bacterium that contains more than one DNA molecule, we must establish that__

the additional molecules are not plasmids before concluding that the species has a multipartite genome

This is easy enough with many bacteria, including E. Coli, which __, none of which is more than a few kb in size and none of which__

harbors various combinations of plasmids

carry genes essential for survival of the bacterium

With other bacteria, the distinction is not so easy. Ex: Vibrio cholerae: the pathogenic bacterium has two circular DNA molecules, both of which carry essential genes, although most of those specifying the central cellular actigities as well as the genes that confer pathogenicity, are located on the __

larger molecule

The smaller molecule contains an __, a set of genes and other DNA sequences that enable plasmids to capture genes from bacteriophages and other plasmids

The smaller molecule appears to be a __ rather than a __

integrin

plasmid rather than a chromosome

Complications that arise in bacteria such as Vibrio led to the term __to describe a __. This means that we now do what?

chromid

plasmid that carries essential genes

distinguish between three, rather than just two, types of DNA molecule that might be found in a bacterium

What are the three?

First, there are one or more bacterial chromosomes, carrying essential genes and located in the nucleoid

The second are genuine plasmids, which are distinct from a bacterial chromosome because of their special plasmid partitioning system and whose genes are nonessential to the bacterium

Third are the chromids, which use a plasmid partitioning system but which carry genes that the bacterium needs to survive